I cheated on my fiance with somone...now I don't want to marry him, no, i haven't told him yet?

I met this guy at book store acouple of times and he and I were instantly attracted to each other. One day we hat lunch together, I tried not to see him anymore but the attraction was so strong. After lunch he walked me to my car and kissed me. Let me tell, it was the most amazing kiss EVER. It so F-ing pion and it difinitely did leave me breathless. My first kiss with my fiance was, okay it toook some getting use to to get us into right synch. Driving home that night wasn't easy, i could barely focus on the road. I felt like a different person. I barely have with my fiance, subconiously I think i seeking to feel what I felt with that guy. No, I didn't sleep with that guy, I have bn avoiding him...its bn a 2 months, I still think so strongly of him and wanting him. What does this mean???Please help